Transparent Mesh when rendering
You have a foreground and a background render layers. The background layer is setup to multiply shadows over the video layer (that's why the butteflies look like... shadows). The foreground is set up as alpha over and it should be the one that combines your scene color information over the background using an alpha channel. The issue is that your foreground layer is empty! You are rendering the contents of an empty layer and using the only layer that contains information as a mask!



Instead of an empty layer, use the layer that contains your scene.